Technical Field
The disclosure relates to a recovery device and a recovery method for recovering a specific material as a dewatering aid from sludge, and a sludge dehydration system and a sludge dehydration method in which the dewatering aid recovered from sludge is added to difficult-to-dewater sludge to dewater the sludge.
Related Art
Difficult-to-dewater sludge generated in sewage treatment plants or the like is low in fiber components and exhibits poor dewaterability. Dewatering is performed on difficult-to-dewater sludge such as digested sludge in which organic matter (fiber components and the like) in sludge is decomposed by the action of anaerobic bacteria and excess sludge in which the organic matter is converted to microorganisms. Accordingly, fiber components are reduced in sludge before dewatering. Fiber components in sludge function as flocculation nuclei, and have the effect of forming waterways in flocs during dewatering. Thus, sludge containing reduced fiber components cannot appropriately flocculate, and therefore exhibits poor dewaterability.
There is a method in which difficult-to-dewater sludge is dewatered by mixing fibrous matter or plant material such as sawdust or chaff as a dewatering aid into the difficult-to-dewater sludge to compensate fiber components reduced by the decomposition of sludge. The addition of even a small amount of fibrous matter used as a dewatering aid enables a dewatered cake with a low water content to be stably obtained, and, in the case of pressure dewatering, improves the detachability of a dewatered cake. However, in the case of this method, since a large amount of dewatering aid must be prepared and supplied, running cost increases, and facilities for stockpiling and supplying the dewatering aid must be installed.
To cope with this, Japanese Patent Application Publication No. S61-268400 discloses a technique of separating and recovering fiber components in raw sludge generated in a primary sedimentation tank of a sludge treatment process, and adding the fiber components to difficult-to-dewater sludge such as excess sludge or digested sludge.
Published Japanese Translation of PCT International Application No. 2000-513267 discloses a recovery device in which different components in a multiple layer material are crushed into small pieces with opposed disks rotating relative to each other and in which readily pulped pieces of materials are separated with a perforated drum, and the remaining small pieces are discharged from one end of the drum with the aid of a screw feeder in the drum in a later stage.
In Japanese Patent Application Publication No. 2012-71296, to lower the water content of a dewatered cake, a dewatering aid using synthetic fibers is prepared by carefully selecting or designing a material, diameter, length, and shape, and is added as an optimum dewatering aid to sludge.
Japanese Patent Application Publication No. 2012-206018 discloses a sludge management system for managing a sludge dewatering process in which sludge supplied to a dewatering facility is dewatered with the addition of a dewatering aid.